This invention relates generally to rating plugs for electronic trip units in circuit breakers, and more particularly, this invention relates to a world wide web enabled rating plug for modifying the rating plug via the world wide web and a digital rating plug that has a programmable memory for storing scaling and optioning data.
Circuit breakers are widely used to protect electrical lines and equipment. The circuit breaker monitors current through an electrical conductor and trips to interrupt the current if certain criteria are met. One such criterion is the maximum continuous current permitted in the protected circuit. The maximum continuous current the circuit breaker is designed to carry is known as the frame rating. However, the breaker can be used to protect circuits in which the maximum continuous current is less than the circuit breaker frame rating, in which case the circuit breaker is configured to trip if the current exceeds the maximum continuous current established for the particular circuit in which it is used. This is known as the circuit breaker current rating. Obviously, the circuit breaker current rating can be less than but cannot exceed the frame rating.
An electronic trip unit (xe2x80x9cETUxe2x80x9d) is a device that is used in conjunction with an electromechanical circuit breaker to control the current verses time trip response. The time versus current trip characteristics are, in part, a function of the maximum continuous current permitted by the circuit breaker. This maximum continuous current is also called the current rating of the circuit breaker. As long as the current remains below this maximum continuous current rating, the breaker will remain closed. Momentary low magnitude excursions above the rated current are tolerated; however, persistent overcurrents result in tripping of the breaker. The time delay and generation of the trip signal is an inverse function of the magnitude of the current. For very large magnitude overcurrents, such as would be produced by a fault, the microcomputer is programmed to generate a trip signal instantaneously.
The modification of the current vs. Trip time response curve is a serious matter. For safety purposes, the circuit breaker must be properly configured to provide the type of protection judged by the customer or plant engineer to be appropriate. Therefore the modification to this protection must also be considered to be a very serious event and handled in a way that prohibits errors.
Typically, the circuit breaker current rating is set by a rating resistor (a xe2x80x9cburden resistorxe2x80x9d) which is selected to generate a preset voltage when a current proportional to the maximum continuous current permitted in the protected circuit passes through the rating resistor. In order to provide for adjustment of the current rating so that the circuit breaker can be used to protect circuits with different maximum continuous currents, it is known to incorporate the rating resistor in a replaceable rating plug which may be selectively inserted into the breaker.
Field replaceable rating plugs are known. These plugs are field installable and may be mechanical for use with thermal-magnetic trip units or may use a combination of analog circuit scaling and digital techniques to change the ETU response. It is typical for these plugs to provide mechanical rejection of plugs that are not suited to certain ranges or frame sizes.
In current designs of ETU it is typical to utilize an electronic signal scaling method that was either completely analog or a combination of analog and digital methods. Scaling of current sensor signals with resistors is an error prone technique. These resistors are placed on the plug-in module that uses an electrical connector. These connectors have a contact resistance that becomes part of the circuit. The variation in the connector resistance can cause error in the analog circuit.
Electronic trip circuit interrupters are designed to interrupt overcurrent conditions over a wide range of ampere ratings. The current through the protected electric power circuit is continuously sensed by means of current transformers and a voltage signal is supplied to the signal processor within the ETU circuit by means of so-called xe2x80x9cburden resistorsxe2x80x9d, such as rating resistors in a rating plug. The size of the burden resistor accordingly sets the ampere rating of the corresponding circuit interrupter. A common electronic circuit interrupter could therefore operate over a wide range of ampere ratings by merely changing the value of the burden resistor within the electronic trip circuit. It is important to prevent an electronic circuit interrupter from being inserted within an electrical distribution circuit for which the circuit interrupter is over-rated. It is perhaps equally important not to insert a circuit interrupter within an electric power distribution circuit for which the circuit interrupter is under-rated, as so-called xe2x80x9cnuisance-trippingxe2x80x9d could occur. It is also important to insure that a circuit interrupter is not inserted within an electric power distribution circuit with no rating plug or burden resistor whatsoever.
Another problem with scaling those use resistive circuits is that there needs to be many different circuit variations with different valued resistors for each range. Currently, it is known to use resistors for analog circuit scaling and digital techniques that indicate to a microprocessor that there is a resistor in the scaling circuit of a specific value. Then the microprocessor can recalibrate its response based upon this resistor value. Errors, however, are commonplace with analog methods that use resistors.
U.S. Pat. No. 4,958,252 to Murphy discloses a removable rating plug having memory. The memory is used to store service data of the circuit breaker for determining its mechanical wear and electrical damage. For reading the number of operations of the operating mechanism and the trip history of the circuit breaker, or for changing information in the rating plug, the rating plug must be removed from the circuit breaker and plugged into a programmer device. Not only does this interrupt service of the circuit breaker, but it also necessitates the services of a skilled on-site technician.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a system for changing the rating plug information of a circuit breaker, the system comprising a circuit breaker having an electronic trip unit, a microcomputer in the electronic trip unit, and a rating plug having a non-volative memory storing current rating and frame rating of the circuit breaker, a first internet connection for connecting the circuit breaker to the world wide web, a vendor subsystem, and, a second internet connection for connecting the vendor sub-system to the world wide web, wherein the vendor sub-system and the microcomputer are communicable via the first and second internet connections for altering current rating of the circuit breaker by sending new data from the vendor sub-system to the microcomputer and then to the non-volative memory.
The above discussed and other drawbacks and deficiencies are also alleviated by a plug-in digital rating plug for an electronic trip unit of a circuit breaker, the rating plug comprising a housing, a connector for connecting the rating plug to the electronic trip unit, and, a non-volatile memory storing current rating of the circuit breaker, wherein the rating plug sends only digital information to the electronic trip unit.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.